The determination of directions, angles, and lengths as positions is required in many fields of application, for example, in geodetic and industrial surveying. Developments in angle measuring technology have led via mechanical readout procedures up to fully automated angle measurement according to the current prior art.
Known automated position measuring apparatuses generally comprise a code carrier and a scanning device. In angle measuring devices, the code carrier is typically implemented as rotatable about an axis relative to the scanning device, wherein then an angle position of the code carrier represents the variable to be measured. The code carrier can have, for example, an indexing or coding for position determination, wherein the coding can be applied to a surface or lateral surface of the code carrier.
To automatically detect the position, the code carrier, which is movable relative to the scanning device, is scanned by means of various technologies. The known scanning methods include electronic-magnetic, electronic, and optical-electronic methods. The following statements relate to optical-electronic scanning methods and scanning devices, which have in particular an illumination device and a corresponding detector.
Typical optoelectronic angle sensors for determining a rotational angle about an axis have a code carrier and an optical detector, which are rotatable relative to one another. The optical detector is, for example, a photodetector, a CCD line array, or a CCD surface array. The code carrier is generally implemented as a circular disc or circular ring, and carries an optically detectable position code along the circumference thereof, of which a section is imaged by an illumination device on the detector. In general, the code carrier of the angle sensor rotates. However, it is also possible to implement the code carrier as stationary and the detector as rotating.
To determine angular positions from 0° to 360°, the coding is typically arranged in a full circle. The angle resolution of the full circle is determined according to the type of coding and according to the scanning device used for reading the coding. Thus, for example, by applying a code in a plurality of tracks or by finer indexing, the angle resolution is increased, wherein the achievable resolution is restricted for reasons of manufacturing and costs. For example, arrangements of one or more detectors are known for reading the code, CCD line arrays or CCD surface arrays can represent such detectors, for example. The code can be implemented by structuring a reflective surface or also a translucent material, so that the imaging is performed in transmission, reflection, or a combined method.
The Swiss patent specification CH 658514 A5 discloses such an apparatus for measuring an angle position. A mark, the position of which in relation to a surface of sensors represents the variable to be measured, is imaged on this surface. The output signals of the sensors are led into an analysis circuit, which sequentially determines the distribution of the intensity of the signals generated by the sensors. The position of the mark in relation to the surface of sensors can be derived from the intensity distribution.
The dimensions of a position measuring apparatus for geodetic devices are advantageously to be kept small. To permit a corresponding small and less cumbersome construction, the illumination device and the detector of the position measuring apparatus have for some time been arranged on a shared electrically powered printed circuit board, and not, as beforehand, above and below a code carrier respectively on a separate electrically powered printed circuit board. In the case of position measuring apparatuses of the prior art, having an arrangement of the detector and the illumination device located adjacent to one another, the emitted beams are deflected by a deflection element having two planar, reflective surfaces, for example, such that an image of the code is generated on the detector by the code carrier, which is arranged downstream in the beam path. The emitted beams can optionally be collimated by means of an optic arranged directly downstream from the illumination source.
Since a code carrier is to be guided as closely as possible over the detector, the most planar and smooth surface is an essential mechanical requirement. In addition, high-precision lateral positioning of source and receiver must be performed.
The positioning of the chips in the component housings can be scattered significantly by manufacturing tolerances, so that an exact position of the chips itself cannot be insured by the positioning of the overall component. These problems relate in particular to the beam source.
Placing the beam source and the detector adjacent to one another on the same plate allows a calibration of sensor and source with the aid of a microscope. Both components conventionally have different structural heights. Thus, the radiation source normally has a greater depth than the detection element.